Recent developments in the administration of drugs in forms which control the release of the drug include biodegradable polylactide implants such as those disclosed in European Patent Application No. 82300416.3; beeswax implants for the administration of growth hormone (oGH) as described by S. L. Davies, et al, in The Journal of Dairy Science, Vol. 66, No. 9, pp 1980-1981 (1983); a cholesterol matrix delivery system for the sustained release of macromolecules, including a variety of growth hormones, which is described in U.S. Pat. No. 4,452,775; subdermal sustained release implants containing microencapsulated drug in a matrix as described in U.K. Pat. No. GB 2,103,927; slow release implants of Zn-DTPA as described in chemical abstracts CA 90(20):15704IV; and orally administered composition of morphine in lipids as described by K. S. Chang, et. al., in J. Pharm. Sci., 69(4), 466-9. Injectable sustained release compositions include biodegradable polymer microcapsules containing aqueous solutions of polypeptides which are described in European Patent Application No. 81305426.9, a crystalline carbohydrate nanosphere matrix described by U. Schroder, J. Immunological Methods 70, 127-132 (1984), and prolonged release nonaqueous compositions of polypeptides which are preferably associated with metals or metal compounds which may additionally contain antihydration agents dispersed in biocompatible oils, which are described in European Patent Application No. 85870135.2, published Apr. 4, 1986.
Methods for the preparation of pharmaceutical compositions include, a process for the preparation of pharmaceutical compositions which exhibit retarded liberation of active material utilizing both a high melting and a low melting lipid of lipoid and embedding the active ingredient at a temperature greater than the temperature of the low melting component prior to tableting, which is described in U.S. Pat. No. 4,483,847; and a process for the preparation of amino acid containing microcapsules which is described in U.S. Pat. No. 3,726,805. A general process for encapsulating or coating solid particles or viscous liquid droplets is described in International Patent Application PCT/US No. 85/00827 and a method for the preparation of wax-particles is described in UK patent application GB No. 2,088,274.
It is clear from the above references that there is considerable interest in providing dosage forms of biologically active substances which release the substance in a controlled manner and, thus, reduce the frequency of administration.
The development of sustained release compositions of biologically active macromolecules presents special problems due to their complex modes of action and intricate structures. The development of sustained release compositions containing biologically active macromolecules such as growth hormones, which do not interfere and/or interact with these hormones resulting in compositions which are either inactive or do not provide the expected level of biological response, is required. It is an object of the present invention to provide compositions of biologically active proteins, peptides and polypeptides such as growth hormones, which are suitable for parenteral administration. It is another object of this invention to provide a method of increasing and maintaining increased levels of growth hormones in the blood of treated animals and humans for extended periods of time and obtaining beneficial effects such as increasing weight gains, increasing milk production in lactating animals, increasing growth rate, increasing feed efficiency, increasing muscle size, decreasing body fat and improving the lean meat to fat ratio by parenteral administration of the compositions of the invention.